The long-term goal of this project is to characterize a novel pathway for the nuclear packaging and export of ultra-large ribonucleoprotein granules (megaRNPs) and its impact on synapse assembly. A long-standing tenet of cellular biology has been that all nucleo-cytoplasmic traffic takes place through the nuclear pore complex (NPC). Using the Drosophila neuromuscular junction (NMJ) as a model system, however, we recently uncovered an alternative pathway for the nuclear export of megaRNPs. This NPC- independent pathway has the potential to fundamentally change our understanding of nucleo-cytoplasmic communication. In this pathway, transcripts are packaged in megaRNPs within the nucleus and are exported to the cytoplasm by budding through nuclear envelope membranes in a process akin to the nuclear egress of Herpes-type viruses. The proposed project represents an incisive approach to understand the impact of this pathway on cellular biology, with a focus on synapse formation. We will investigate the protein and mRNA composition of megaRNPs, and determine if megaRNPs are assemblages of multiple or single mRNAs species. We will use molecular genetic tools in Drosophila to determine the significance of megaRNP composition in transcript localization and proper synapse assembly. We will also determine the relationship between nuclear envelope budding and NPC-dependent modes of mRNA export. Finally, we will begin an analysis of the nuclear envelope budding pathway in mammalian cells. These studies are likely to be paradigm-shifting for our understanding of how and where large RNP transport granules are formed, which is elemental to the understanding of how the precise polarized assembly of cellular macromolecular complexes is achieved. In addition, these studies will elucidate novel biological pathways that will almost certainly lead to new clinical strategies for the treatment of laminophathies such as Emery-Dreifuss muscular dystrophy, movement disorders such as dystonia, and Herpes virus-type infections.